// Triangulator is from http://www.unifycommunity.com/wiki/index.php?title=Triangulator

using System.Collections.Generic;
using UnityEngine;

public class tk2dTriangulator
{
	private List<Vector2> m_points = new List<Vector2> ();

	public tk2dTriangulator (Vector2[] points)
	{
		m_points = new List<Vector2> (points);
	}

	public int[] Triangulate ()
	{
		List<int> indices = new List<int> ();
		
		int n = m_points.Count;
		if (n < 3)
			return indices.ToArray ();
		
		int[] V = new int[n];
		if (Area () > 0) 
		{
			for (int v = 0; v < n; v++)
				V[v] = v;
		} 
		else 
		{
			for (int v = 0; v < n; v++)
				V[v] = (n - 1) - v;
		}
		
		int nv = n;
		int count = 2 * nv;
		for (int m = 0, v = nv - 1; nv > 2;) 
		{
			if ((count--) <= 0)
				return indices.ToArray ();
			
			int u = v;
			if (nv <= u)
				u = 0;
			v = u + 1;
			if (nv <= v)
				v = 0;
			int w = v + 1;
			if (nv <= w)
				w = 0;
			
			if (Snip (u, v, w, nv, V)) 
			{
				int a, b, c, s, t;
				a = V[u];
				b = V[v];
				c = V[w];
				indices.Add (a);
				indices.Add (b);
				indices.Add (c);
				m++;
				for (s = v,t = v + 1; t < nv; s++,t++)
					V[s] = V[t];
				nv--;
				count = 2 * nv;
			}
		}
		
		indices.Reverse ();
		return indices.ToArray ();
	}

	private float Area ()
	{
		int n = m_points.Count;
		float A = 0.0f;
		for (int p = n - 1, q = 0; q < n; p = q++) 
		{
			Vector2 pval = m_points[p];
			Vector2 qval = m_points[q];
			A += pval.x * qval.y - qval.x * pval.y;
		}
		return (A * 0.5f);
	}

	private bool Snip (int u, int v, int w, int n, int[] V)
	{
		int p;
		Vector2 A = m_points[V[u]];
		Vector2 B = m_points[V[v]];
		Vector2 C = m_points[V[w]];
		if (Mathf.Epsilon > (((B.x - A.x) * (C.y - A.y)) - ((B.y - A.y) * (C.x - A.x))))
			return false;
		for (p = 0; p < n; p++) 
		{
			if ((p == u) || (p == v) || (p == w))
				continue;
			Vector2 P = m_points[V[p]];
			if (InsideTriangle (A, B, C, P))
				return false;
		}
		return true;
	}

	private bool InsideTriangle (Vector2 A, Vector2 B, Vector2 C, Vector2 P)
	{
		float ax, ay, bx, @by, cx, cy, apx, apy, bpx, bpy,
		cpx, cpy;
		float cCROSSap, bCROSScp, aCROSSbp;
		
		ax = C.x - B.x;
		ay = C.y - B.y;
		bx = A.x - C.x;
		@by = A.y - C.y;
		cx = B.x - A.x;
		cy = B.y - A.y;
		apx = P.x - A.x;
		apy = P.y - A.y;
		bpx = P.x - B.x;
		bpy = P.y - B.y;
		cpx = P.x - C.x;
		cpy = P.y - C.y;
		
		aCROSSbp = ax * bpy - ay * bpx;
		cCROSSap = cx * apy - cy * apx;
		bCROSScp = bx * cpy - @by * cpx;
		
		return ((aCROSSbp >= 0.0f) && (bCROSScp >= 0.0f) && (cCROSSap >= 0.0f));
	}
}
